diff --git a/packages/elements/__tests__/prompt-input.test.tsx b/packages/elements/__tests__/prompt-input.test.tsx
index d961a3ba..ce89183c 100644
--- a/packages/elements/__tests__/prompt-input.test.tsx
+++ b/packages/elements/__tests__/prompt-input.test.tsx
@@ -704,6 +704,51 @@ describe("promptInputTextarea", () => {
     expect(onSubmit).not.toHaveBeenCalled();
   });
 
+  it("does not submit on Enter while streaming - #439", async () => {
+    setupPromptInputTests();
+    const onSubmit = vi.fn();
+    const user = userEvent.setup();
+
+    render(
+      <PromptInput onSubmit={onSubmit}>
+        <PromptInputBody>
+          <PromptInputTextarea />
+          <PromptInputSubmit onStop={vi.fn()} status="streaming" />
+        </PromptInputBody>
+      </PromptInput>
+    );
+
+    const textarea = screen.getByPlaceholderText(
+      "What would you like to know?"
+    );
+    await user.type(textarea, "Test");
+    await user.keyboard("{Enter}");
+
+    expect(onSubmit).not.toHaveBeenCalled();
+  });
+
+  it("does not submit on Enter without a submit button - #439", async () => {
+    setupPromptInputTests();
+    const onSubmit = vi.fn();
+    const user = userEvent.setup();
+
+    render(
+      <PromptInput onSubmit={onSubmit}>
+        <PromptInputBody>
+          <PromptInputTextarea />
+        </PromptInputBody>
+      </PromptInput>
+    );
+
+    const textarea = screen.getByPlaceholderText(
+      "What would you like to know?"
+    );
+    await user.type(textarea, "Test");
+    await user.keyboard("{Enter}");
+
+    expect(onSubmit).not.toHaveBeenCalled();
+  });
+
   it("does not submit on Enter during IME composition - #21", () => {
     setupPromptInputTests();
     const onSubmit = vi.fn();
diff --git a/packages/elements/src/prompt-input.tsx b/packages/elements/src/prompt-input.tsx
index 412c846d..86ce866a 100644
--- a/packages/elements/src/prompt-input.tsx
+++ b/packages/elements/src/prompt-input.tsx
@@ -983,12 +983,15 @@ export const PromptInputTextarea = ({
         }
         e.preventDefault();
 
-        // Check if the submit button is disabled before submitting
+        // Check if the submit button is disabled before submitting.
+        // No submit button in the form means the input is not submittable
+        // right now (e.g. PromptInputSubmit renders as a stop button while
+        // streaming), so block Enter in that case too.
         const { form } = e.currentTarget;
         const submitButton = form?.querySelector(
           'button[type="submit"]'
         ) as HTMLButtonElement | null;
-        if (submitButton?.disabled) {
+        if (!submitButton || submitButton.disabled) {
           return;
         }